One example cellular communications system is Universal Mobile Telecommunications Systems, UMTS, Wideband Code Division Multiple Access, W-CDMA. Wireless communication systems following UMTS technology, were developed as part of Third Generation, 3G, Radio Systems, and is maintained by the Third Generation Partnership Project, 3GPP. A mobile radio communication system, such as a UMTS type system, includes a mobile radio communication network communicating with wireless devices, also known as mobile terminals or user equipments, UEs and with external networks. The UMTS network architecture includes a Core Network, CN, interconnected with a UMTS Terrestrial Radio Access Network, UTRAN, via an Iu interface. The UTRAN is configured to provide wireless telecommunication services to users through mobile radio terminals, referred to as user equipments, UEs, in the 3GPP standard, via a Uu radio interface. A commonly employed air interface defined in the UMTS standard is W-CDMA. The UTRAN has one or more radio network controllers, RNC, and base stations, referred to as Node Bs by 3GPP, which collectively provide for the geographic coverage for wireless communications with UEs. Uplink, UL, communications refer to transmissions from UE to Node B, and downlink, DL, communications refer to transmissions from Node B to UE. One or more Node Bs are connected to each RNC via an Iub interface; RNCs within a UTRAN communicate via an Iur interface. An example block diagram of an UMTS WCDMA is shown in FIG. 1.
Radio transmitters are generally limited in total transmit power, a limit imposed by regulatory agencies or by the battery or power amplifier technology. This power limitation may result in reduced radio coverage. For example, as user equipment, UE, moves away from its Node B base station, it typically increases its transmission power to maintain the same level of quality at the base station. The UE output power is controlled by the Node B base station via one or more power control loops. When the UE reaches a maximum power and may no longer increase its power to maintain the signal quality desired at the base station, power scaling is applied. This may occur for example when the UE is close to cell-edge, or when the UE enters a region of deep signal fade.
Mobile networks with High Speed Packet Access, HSPA, include High Speed Downlink Packet Access, HSDPA, and High Speed Uplink Packet Access, HSUPA, or Enhanced Uplink, EUL. The enhanced uplink introduces two new code-multiplexed uplink physical channels: an enhanced data channel, E-DCH Dedicated Physical Data Channel, E-DPDCH, and an enhanced control channel, E-CCH Dedicated Physical Control Channel, E-DPCCH. In EUL, the Dedicated Physical Control Channel, DPCCH, carries pilot, power control, and Inner Loop Power Control, ILPC, information. The transport format of EUL is designated as E-DCH Transport Format Combination, E-TFC. A standard E-TFC table is set forth in 3GPP specification 25.321. A transmit power gain factor named βed is used to indicate the enhanced data channel E-DPDCH amplitude for each E-TFC in the table, and a transmit power gain factor named βec is used to indicate the amplitude of E-DPCCH. The power level of the DPDCH is indicated by βd for each transport format, and the parameter βc is used to indicate the DPCCH transmit power level. A predetermined small minimum transmit power level of E-DPDCH is specified using βed, min in the 3GPP specification 25.214. In the uplink, DPCCH is used as a power reference with the power offset of all the other physical channels being defined relative to the DPCCH power.
A configurable transmit power gain factor βed, min avoids excessive downscaling of the data channel E-DCH power by setting a minimum power level for the E-DCH. The configurable βed, min permits a better trade-off of the power allocation between the E-DCH and the DPCCH control channel during UE power limitation, which in turn improves the EUL coverage. FIG. 2 illustrates power allocated for E-DCH with and without a configurable βed, min.
TS 25.214, “Physical layer procedures (FDD)”, ver. 11.3.0, 2012 Sep. 19, describes current 3GPP power scaling. In subsection 5.1.2.6, power scaling handling when a UE is power limited is described. Subsection 5.1.2.6 sets forth different power scaling procedures which are applied depending on if DPDCH is configured or not, and if E-DCH configured or not. Here, the term “configured” means that physical channel radio resources are reserved for transmission. The configuration when E-DCH is not configured and DPDCH is configured is from now on referred to as configuration 1. The configuration when E-DCH is configured and DPDCH is not configured is from now on referred to as configuration 2. The configuration when both E-DCH and DPDCH are configured is from now on referred to as configuration 3. To say that E-DCH is configured means that one or more E-DPDCH(s) physical channel resources are reserved for uplink transmission from user equipment, UE, to NodeB. Similarly, to say that DPDCH is configured means that one or more DPDCH(s) physical channel resources are reserved for transmission from user equipment, UE, to NodeB.
In the power scaling applied for configuration 1, the power scaling procedures inform the UE, after applying DPCCH power adjustments and gain factors, to apply additional scaling to the total transmit power so that it is equal to the maximum allowed power. DPCCH/DPDCH and DPCCH/HS-DPCCH power ratios are maintained.
In the power scaling applied for configurations 2 and 3 where E-DCH is configured, the user equipment, UE, after applying DPCCH power adjustments and gain factors, first reduces all the E-DPDCH gain factors βed,k by an equal scaling factor to respective values βed,k,reduced so that the total transmit power is equal to the maximum allowed power. Then, power scaling procedures differ depending on whether a DPDCH is configured. In the power scaling applied for configuration 2, where DPDCH is not configured, the power scaling follows a procedure which, depending on a network-configurable transmit power gain factor βed,min sets a limit on how much the user equipment may scale down the E-DPDCH gain factors βed,k. At this point, if the user equipment, UE, transmit power still exceeds the maximum allowed transmit power limit, equal scaling is applied to all channels, similar to what is done for the power scaling applied for configuration 1. This procedure gives the network control over a relative lower bound of the E-DPDCH gain factors βed,k and in turn improves the EUL coverage as described above.
In power scaling applied for configuration 3 where DPDCH also is configured, the power scaling procedure allows downscaling of E-DPDCH gain factors βed,k,reduced down to the “smallest quantized βed,k value” (see the definition in TS 25.214, “Physical layer procedures (FDD)”, ver. 11.3.0, 2012-Sep.-19). If βed,k,reduced is lower than the “smallest quantized βed,k value,” then discontinuous transmission, DTX, of the E-DPDCH(s) is(are) allowed. The DTX procedure secures performance of DPDCH traffic over E-DCH traffic.
EP 1 931 160 A1 relates to a mobile station and communications method. A transmit power control process carried out by the mobile station is disclosed. When an estimated total transmit power is exceeds a Pmax value, a gain factor of E-DPDCH is reduced so as to reduce the total transmit power. ‘Additional channel transmit power scaling’-regions are disclosed where additional channel transmit power scaling is applied in states in which DPDCH data are transmitted.
However, the current 3GPP power downscaling procedures has a negative impact on DCH performance and causes un-due power scaling of E-DCH traffic.